Method of simultaneously springing two girders



Jan. 17, 1956 A. LlPSKl 2,730,797

METHOD OF SIMULTANEOUSLY SPRINGING TWO GIRDERS Filed July 21, 1952 2 SheetsSheet 1 INVENTOR. a broutbm {/705/k/ United States Patent METHOD OF SIMULTANEOUSLY SPRINGING TWO GIRDERS Abraham Lipski, Brussels, Belgium Application July 21, 1952, Serial No. 300,049

Claims priority, application Belgium July 25, 1951 Claims. (Cl. 29-452) This invention relates to a method for simultaneously bending two rigid metal reinforcements, which by themselves, are resistant to bending. More specifically the invention relates to a method for simultaneously bending two identical rigid metal girders which are each able to constitute a part of a beam comprising precompressed concrete and a pre-bent rigid metal girder, comprising atranging the two rigid metal girders in such a manner that their mean planes in which they will bend under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girder in such a manner that the ends of each girder are free to move towards each other if the girders are bent, maintaining locally the two girders at a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stiffening said girders in the proximity of said cross-pieces, bracing the stiffened portions of the girders and the projecting portions of the cross-piece situated in their proximity, approaching the adjoining ends of the girders, in order to bend the two girders in the direction in which they will bend under the action of the service loads, maintaining the girders in their pre-bent position, by means acting on the next portions of said adjoining ends, and supporting the projecting portions of said crosspieces at such a level that the whole is at a distance from the ground.

In the copending application No. 221,967, applicant proposed to bend rigid metal reinforcements for prestressed reinforced concrete beams in the direction in which they will bend under the effect of the service loads, and to prevent these reinforcements thus bent from returning to their initial position, by causing concrete to adhere to at least one portion of the fibres of the reinforcements, the stresses of which caused duringthe service are tensions.

More particularly, he proposed to bend two reinforcements of this kind simultaneously by approaching their extremities whilst maintaining their middle part at a constant distance. He has also proposed to approach the middle of the two reinforcements whilst the extremities are maintained at a constant distance. ln the case where the extremities are approached towards each other, the reinforcements can, of course, be caused to bend by maintaining them at a constant distance at other points than in their middle, more particularly at one quarter of their length from each extremity.

The object of the present invention is to provide a particular method of construction of the above men tioned cross-piece combined with other characteristics which will facilitate the handling of the reinforcements when they are joined together, as well as the placement of the iron work, the encasing, and concreting of the beams of pre-bent reinforced concrete of which the reinforcements in question form a part.

For this purpose, in the equipment according to the invention the above mentioned cross-pieces are arranged in such a way as to project laterally with respect to the reinforcements to be bent.

The parts of the cross-pieces which project laterally relatively to the reinforcements to be bent serve as supporting member with a view to:

(1) The placement of the set of the two reinforcements which have been bent, leaving free along their whole length the fibres to which the concrete is intended to adhere; this eliminates any obstacle to the placing of a continuous casing and of continuous secondary bars for the concrete;

(2) The attachment of the set of the two reinforce ments in all displacements and handlings.

These cross-pieces are advantageously connected together by tighteners to stiffening means, which are kept applied against the core of the reinforcement. They then form part of a bracing intended to prevent any lateral slipping away or buckling of the different elements of the two reinforcements.

in the case of the simultaneous bending of two reinforcements by the approach of certain of their parts whilst other parts are maintained at a constant distance, use may advantageously be made for effecting this approach of an equipment which comprises two traverses united together by two screw-threaded rods provided with screw nuts, one of these traverses being so arranged as to lean against one of the reinforcements to be bent whilst the other traverse serves as a support to a jack, the thrust of which is transmitted to the other rein- 1 for-cement to be bent.

In order to prevent the separation of the corresponding parts of the two rigid metal reinforcements which have been bent one towards the other by the approach of certain parts whilst other parts were maintained at a constant distance by cross-pieces, use is preferably made of an equipment which comprises on the one and the other side of the web of each of the reinforcements at the points to be maintained approached one to the other after bending of the reinforcement, stiffening means, which are kept applied against the web of the same and provided with sole-plates which project laterally relatively to the reinforcements, the sole-plates pertaining to stiffening means situated on the same side of the reinforcements being connected together by ties of adjustable length.

With such an equipment the ties intended to prevent the separation of the reinforcements until the concrete has become set are much shorter than the bolts forming part of the equipment above suggested for effecting the the approach of these parts by means of hydraulic jacks.

When the ties above mentioned consist of rods screwthreaded in two opposite directions, this equipment itself can serve as a means for bending the reinforcements, if it is found satisfactory to calculate the forces applied thereto on the basis of the deformations to which they are subjected. It also permits of stopping the effort that caused the bending without the intervention of jacks.

In order to avoid the above mentioned ties of adjustable length being subjected to bending in a plane parallel to the bending plane of the two reinforcements, owing to the angle made after bending by the parts of the reinforcements where the above mentioned sole-plates of the stiffening means shall have concave surfaces, the section of which by a plane parallel to the plane where the bending is effected is a circumference, and that on these sole-plates rest, by complementary convex surfaces screw-nuts which engage with rods screw-threaded in two opposite directions and which traverse the sole-plates with play.

other;

inafter described with reference to theaccompanyingdrawings illustrating diagrammatically and by way of example various forms of construction of theequipment according to; the invention.

Figure l is an elevation showing diagrammatically a pair of, reinforcements. to be bent and; an equipment intended to maintain constant the distance between certain points of the two rigid metal reinforcements, the extremities of which have to be approached towards each Figure 2 is a side view of the reinforcements and of the equipment shown inFignre 1;

Figure 3 is a view similar to. the one illustrated in Figure 2 and's'howing the set suspended;

Figure 4 is another view similar to Figure 2, showing the set resting on supports whieh rnaintain the lower sole-piece of theflower reinforcement free of any contact along, its. whole length;

Figure 5 is a side view of a pair of reinforcements and of an equipment intended to approach certain points of the two 'metal"reinforcernen ts and to maintain these points at a constant distance after bending of the reinforcements;

' Figure 6" shows. two reinforeements andanother equip ment intended'for the same. action as that shown in Fig: ure 5;

Figure 7 is an elevation. of a parto f the set shown in Figure 6, being at; right angles to that shown in the latter figure;

Figure 8 illustrates, like Figure 2, a modification of an equipment having the same action as that shown. in. Figures land2';

Figure 9' illustrates, like Figure 1, part of the set. illustrated in Figure 8;

Figure 10 shows an. equipment intended to approach certain points, for example the extremities of twometalreinforcements and to maintain these. extremities at a. constant distance after bending ofthe reinforcements;

Figure ll is a section taken along the broken line XI-XI of Figure. 10;

Figure l'2'is a plan view ofamemben shownin Figures 10 and ll; and

Figure 13 shows, partly in section, a, side view of an other modification of the equipment: illustrated in Fig? ure 5.

In all these figures, to indicate,identicalpartsthe same references are used: 7

Referring to the drawings, 2 and '3 in Figure 1 are two rigid metal reinforcements which, even by. themselves, resist bending, These reinforcementsareof I.-scctio,n prfile, They are 'separatedf'rom eaehother by cross piecesl 4, which'are also.ofjl sectionprofilef As. can be seen from- Figure 2; these cross-pieces 4, projectlaterally, relatively to thereinforcemetns 2 and 3.. The lower reinforcement 2 rests. on supports 5. V

The cross-pieces. 4 andthe supports are arrangedat one quarter of, the length ofthe reinforcements 2 and 3 reckoned from eachone of the extremities thereof. The reinforcements 2 and 3 have to be bent by. approaching their extremities. 'During their bending there. is the risk ofbnckhng. In order to avoid this, stiffening means6 are disposed on one and the. other; side of the webs of the reinforcements 2 and 3, These ,stitfening means.

. by means: of-bolts 8" (Figure 2) traversingthe same.

The Setconstituted by thc elements 2' to.4 and 6 to. 8 may easily. be manipulated, for instance. by being. suspended-.- by. chains" 9:

(Figure-3') of-'a rolling bridge. t.

may also be supported by supports (Figure 4) higher than thesupports- 5 in- Figures 1 and" 2; so as to facilitate the placement of the iron work, the encasing and the concreting, while the reinforcements 2 and 3 are maintained bent, of the parts thereof subjected to tension owing to the bending,

The cross-pieces 4 are provided, as shown in Figures 1 and. 2, with; ar.ched supports.11 which allow the. angle that the reiuforcementstihcontact with the supports form with the corresponding crossrpieces to be changed. These arched supports form in traverse section a rounded boss at the point; that comes; in contact with the correspond ing crosspiece'tl. Flats 12 are interposed between one of the sole-pieces of' one of the two cross-pieces 4 and the reinforcementwhich;is;in= contact withthe arched support 11 of this sole-piece, in order to prevent the rocking of the cross-piece relatively to the reinforcement in contact. with. the fiats 12 This prevents the set of the reinforcements 2 and. 3. and. of. the crossvpieces 4. being i in, unstable equilibrium.

In order to approach. therextremities. of, the. two rein-.

forcements, 2 and 3, maintained. locally at aconstant distance by the cross-pieces 4, use may be made of an equipment. usch as, shown in Figure 5. This equipment Comprises two. traverses13 and 14. connected. by two screw-threaded rods 15 and 16. engaged with screw-nuts 17.

The. traverse 13 is. supported. on the; reinforcements 3, whilst, the traverse 14, serves as a support. to a jack 18,. the. piston. of which is. indicated at 19. The. thrust of this jackis transmitted to the reinforcement 2 through theqintermediary. of athird traverse 2%) which slides freely relatively to thescrew-threaded rods; 15 and 16. For this purpose, this. third. traverse is provided. with. holes 21 having a' diameter slightly greater than the outer diameter of the screw-threaded rods 1 5 and 16. These are provided, with screw-threaded parts at points such that by screwing screw-nuts 22 engaging therewith, thalatter can-be drawnagainst the face of the third traverse -opposite thev one by means of which this traverse is in contact withthe reinforcement 2.

When the reinforcements. 2 and 3; have been bent under theactionof the jacky18-19, the screw-nuts 22 are brought against the traverse 2t in such a manner asto keep the reinforcements bent after; removal of the ja k. 7

When. it. is desired. to allow the extremities of the reinforcements 2 and 3 to separate, it suflices to again separatethe third traverse 20 from the traverse M by means of the jack.1819, so that the screw-nuts 22. can be easily unscrewed. The piston:19 is then allowcdto enter into the jack. 18; V

Inorder thatitmay notzbe necessary to fixthe. traverse l3 and 14 as well as the long screw-threaded rods 15- forcementsapproached to one another by means of anequipment,, as illustrated. in Figures 6v and 7. This equipment comprises on. the one andthev other side of the web of each oneof. the reinforcements 2 and 3., at.

the points where the reinforcements have to be maintained close to oneanother. afterbending, stiffening means corstituted by U shaped irons 23, thewebs 2410f which are kept appliedagainstthe webs of. the reinforcements by means. ofbolts,v 2,5? and. the, wings 26, of. which project laterally. with. respect to the, reinforcements. These wingshavetheshap of a trapezium, the large-base of which is soldered to a sole-plate 27.. The lattenprojectslateraliy with respecttothereinforcetnents 2, audit. The

sole-plates 27 pertaining to the stiffening means situated on the same side of the reinforcements are connected together by ties of adjustable length constituted by rods 28 which are screw-threaded in two opposite directions. These sole-plates have concave surfaces 29, the section of which by a plane parallel to the plane in which the bending is effected is a circumference. These surfaces 29 support screw-nuts 30 engaging with the screwthreaded rods 28 which traverse the sole-plates 27 with play. The surface of these screw-nuts which abuts against the surface 29 of the sole-plates 27 is convex and complementary to the surface 29. The surface 29 in Figure 6 is cylindrical, having generatrices at right angles to the plane in which the bending is effected,

During the time that the jack 18-19 approaches the extremities of the reinforcements, the screw-threaded rods 28 are turned in such a manner as to maintain the screw-nuts 30 in contact with the surfaces 29 of the sole-plates 27. When the jack 18-19 is caused to cease to operate, the rods 28 keep the reinforcements 2 and 3 bent until these rods are rotated in the required direction to free the reinforcements from the previous bending effort to which they were subjected.

Being provided with two screw-threads in opposite directions, the rods 28 can serve to bend the two reinforcements by approaching their adjacent extremities without it being necessary to use jacks. In this case, one cannot know the efforts applied to the reinforcements, except by calculation based on the deformations they undergo.

The traverse 13 and 20 of the equipment shown in Figure 5, as well as the traverse 13 and the head of the piston 19 of the equipment illustrated in Figures 6 and 7 are advantageously provided with arched supports 31 similar to the arched supports 11 in Figure 2. These arched supports are provided with spurs 32 intended to engage in holes provided in the sole-pieces of the reinforcements 2 and 3 to be bent. In Figure spurs 33 of the same kind ensure the exact position of the arched supports 31 relatively to the traverses 13 and 29, of the traverse 20 relatively to the piston 19, and of the jack 18 relatively to the traverse 14. In Figure 6, similar spurs ensure the exact position of the arched supports 31 relatively to the traverse 13 and to the piston 19, as well as of the jack 18 relatively to the traverse 14.

Figures 8 and 9 illustrate a modification of the equipment shown in Figures 1 and 2, according to which the cross-pieces instead of being constituted each by an I-scction iron, are constituted by two U-section irons 4' applied on the one and the other side of an iron fiat 11', the width of which is greater than the U-section irons 4, which it separates. The edges of this iron flat 11' are rounded off and thus play the same part as the arched supports 11 shown in Figures 1 and 2.

Figures 10, 11 and 12 illustrate a modification of the equipment according to Figure 6, in which the screwthreaded rods 15 and 16 are guided relatively to the screw-jack 18-19 through the intermediary of a member 34 moving with the screwjack and which slides along these rods. The member 34 carries the support 31 which allows the angle of the reinforcement 2 to be varied with the piston 19. T he member 34 is mounted thereon on the latter in a detachable manner.

The guide 34 prevents the rocking of the rods 15-16 relatively to the jack 18-19 when the effort exerted by the latter would not be directed exactly in the plane passing through the axes of these two rods.

Figure 13 shows a modification of the equipment according to Figure 5, in which the second traverse 14 is mounted on internally screw-threaded members 38 provided with heads 39, against which abuts the traverse 14. The members 38 are screwed on the screw-threaded rods 15, 16 beyond the screw-nuts 22, which abut against the 6 third traverse 20 through the intermediary of which the effort of the jack 18 is transmitted to the reinforcement 2. When the reinforcements 2 and 3 are bent and the screw-nuts 22 have been screwed against the traverse 26 to keep them bending, the members 38 may be unscrewed and they may be removed at the same time as the traverse 14 and the jack 18-19. The removal of these parts facilitates the handling of the group of the two bent reinforcements.

Of course, the invention is not exclusively limited to the forms of construction illustrated, and modifications may be effected as regards the form, the distribution and the constitution of certain parts used in carrying out the invention, provided that these modifications are within the scope of the invention as claimed in the appended claims.

For example the sole-plates 27 may he provided with a spherical supporting surface instead of the cylindrical one mentioned in connection with Figure 7. In this case, the surface of the screw-nuts 30 in contact with these sole-plates must, of course, be spherical so as to be complementary to the spherical surface of the sole-plate.

The screw-threaded rods 15 and 16 may be made integral with a head, as in the case of bolts.

The temporary fixing of the stiffeners 6 and 25 may be effected otherwise than by means of bolts. In certain cases the fixing might be permanent' What I claim is:

l. A method for simultaneously springing two identical rigid metal girders by applying a moment thereto which will deform said girders in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precompressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girder in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said girders in a direction in which they will deform under service loads, maintaining locally the two girders at a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stiffening said girders in the proximity of said cross-pieces, bracing the stiffened portions of the girders and the projecting portions of the cross-piece situated in their proximity, applying a moment to the girders to cause the adjacent ends of the girders to approach each other, in order to spring the two girders in the direction in which they will deform under the action of the service loads, maintaining the girders in their thus sprung position, by means acting on the next portions of said adjoining ends, and supporting the projecting portions of said cross-pieces at such a level that the Whole is at a distance from the ground.

2. A method for simultaneously springing two identical rigid metal girders by applying a moment thereto which will deform said girders in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precompressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girders in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said girders in a direction in which they will deform under service loads, maintaining locally the two girders at a .7 constant distance apart by interposition at a distance from their extremities, o'f cross pieces projecting laterally relatively to the girders, stiffening said girders in the proximity of said cross pie'ce's, bracing thes'tiffened portions of the girders and the projecting "portions of the cross-pieces situated in their proximity, applying a mo ment to the girders to cause the adjacent ends of the girders to approach eachother, by acting on their remote faces, in order to spring thetwoigirders'in the'direction in which they will deform under the action of the service loads, maintaining the-girders in their thus sprung position, by means acting on the anext'portions of said adjoining ends,'rernoving said approachingm'eaus of said ends and supporting the projecting portion's of said crosspieces at such a level that the'whole 'is' at a distance from the ground.

'3. A'methodfor simultaneouslyspringing two identical rigid metal girders by applying a moment thereto which will deformsaidtgirders in the direction in which they will be deformed bya service load preparatory to coating each girder with concrete to form a part of a beam of prec ompressed-concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girders in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said .girders 'inadirection in which they will deform under service loads, maintaining locally the two girders at a constant distance apart by interposition at a 'distance from their extremities, of cross-pieces projecting laterally relatively to the girders, 'stilfening by'removable means only portions of said girders-which will be compressed by bending under the service loads in the proximity of said cross-pieces, bracing the stiffened portions of the girders and theprojecting portions of the crosspieces situatedin their proximity, applying a moment to the girdersto-cause the adjacent ends of'the girders to aprpoach each other, in order to spring thetwo girders in the direction in which they will deform under the action of'the service loads, maintaining the girders in their thus sprungposition by-means acting on the next portions of said adjoining ends, and supporting the'projecting portions of said crosspieces at such a level that thewhole is at a distance from the ground,

4. A method for simultaneouslyspringing two identical rigid metal girders by applying'a moment thereto which will deform 'saidgirdersin the direction in which they will be deformed by a service'load preparatory to coating each girder with concrete to form a part of a beam or precompressed concrete and a thus sprung rigid metal girder, comprisingarrangin gthe two rigid metal girders in such a manner thattheir longitudinal mean planes in which they will deform under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these means planes, arranging also said rigid metal girders in su'ch'a manner that the'ends of each girder are 'free to move towards each other under the application of a moment which will deform said girders in a direction-in which they will deform under service loads, maintaining locally the two girders at a constant distance apart by inter-position at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stiffening said girders in the proximity of said cross-pieces, connecting the stiffened portions of the girders to the projectingportions of the crosspieces situated in theirproxi'inity' by tightener's 'of adjustableleng th, applying'amoment to the girders to cause the adjacent ends of the girders to approach each other, in order to spring the two girders in "the direction in which theywill-defo'rm under theaction of the service loads, 1 maintaming the girders in their thus *sprung" posiiii 8 tion by means acting on the-nextpor-tions of said adjoining cnds, and "supporting: the projecting portions of said cross piec'esat-= such a' level that the whole is at adistancefro'm the ground.

5. A methodfor simultaneously springing two identical rigid metal girders by applying a moment thereto which will deform said girders in the direction in which theywillbedeformedby'a service load preparatory to coating each girder with concrete -to form a partof a beam of Lprecompressed-concrete and a thus sprung rigid inetaitgirder, comprising arranging the two rigid metal girders in such a 'manne'r thattheir longitudinal mean planes in which they will deform under the effect of the service loads co'incide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid-metal :girders in such a manner that the :ends of each :girder are free to move towards each other under the application of a moment which will deform saidfgirders in a direction in which they will deform under service loads, maintaining locally thetwo girders .at-a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively tothetgirders one of these cross-pieces having on each "side'and theother-on' only one side a form pennittinga change in the angle which the girder in contact with this crossrpiece forms with the mean plane of the latter, stiffening said girders in the proximity of-said-cross-piece, bracing the stiffened portions of the girders and the projecting portions of the cross-pieces situated in their proximity, applying a moment to the girders to cause the adjacent ends of the girders to approach each other, in order-to spring the two girders in the direction in which they will deform under the action of the service-loads, maintaining the girders in their thus sprung position by means acting on the next portions of said adjoining ends, and supporting the projecting portions of said cross-pieces at such a level that the whole is at a distance fromthe ground.

6. A method for simultaneously springing two identical rigid metal girders by appying a moment thereto which will deform said girders in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precompressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform under the effect ofthe service loads coincide and that they are symmetrical relatively to aplane perpendicular to these mean planes, arranging "also said rigid metal girders in such a manner that 'the'ends of eac'hgirder are free to move towards ea'ch'other under the application of a moment which will deform said girders in a direction in which they will deform underserv'ice loads, maintaining locally the two girders at'a constant distance apart by interposition at a distance from their extremities, of cross-pieces projectin'g laterally'rel'atively to the girders, stiffening said girders in the proximity of'said cross-pieces, bracing the stiffened portions of the girders and the projecting portions of the cross-pieces situatedin their proximity, applying arched supports against 'theremote faces of the adjoining ends of'the girders in order to permit a change in the angle of the ends of thegirder, applying a moment to the girders to cause'said'arched'supports to be moved towards each other by a hydraulic jack'mounted on a traverse through which pass two threadedrods carrying another traverse applied against one of'the girders, said'jack acting on the remote places of said ends in order to spring the two girders in the direction in 'wh'ich they will deform under the action ofthe service loads, maintaining the girders in their thus sprung position by means acting on the next portions of"sa'idadjoining ends, and supporting the projecting" portions of 'said'crossi-pieces at such a level that the whole 'isat a'tlistancefrom the ground.

7, A method for simultaneouslyspringing two identiavenger cal rigid metal girders by applying a moment thereto which will deform said girders transversely of their longitudinal axis in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precompressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform in a direction transversely of the longitudinal axis of said girders under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girders in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said girders in a direction transverse to the longitudinal axis of said girders, maintaining locally the two girders at a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stiffening said girders in the proximity of said cross-pieces, bracing the stifiened portions of the girders and the projecting portions of the cross-pieces situated in their proximity, applying arched supports against the remote faces of the adjoining ends of the girders in order to permit a change in the angle of the ends of the girder, preventing said arched supports to slide relatively to the ends of the girders, applying a moment to said girders to cause said arched supports to move towards each other by a hydraulic jack mounted on a traverse through which pass two threaded rods carrying another traverse applied against one of the girders, said jack acting on the remote faces of said ends in order to spring the two girders in the direction in which they will deform under the action of the service loads, maintaining the girders in their thus sprung position by means acting on the next portions of said adjoining ends, and supporting the projecting portions of said crosspiece at such a level that the whole is at a distance from the ground.

8. A method for simultaneously springing two identical rigid metal girders by applying a moment thereto which will deform said girders tranversely of their longitudinal axis in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precompressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform in a direction transversely of the longitudinal axis of said girders under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girders in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said girders in a direction transverse to the longitudinal axis of said girders, maintaining locally the two girders at a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stilfening said girders in the proximity of said cross-pieces, bracing the stiffened portions of the girders and the projecting portions of the cross-pieces situated in their proximity, applying a moment to said girders to cause said adjacent ends of the girders to approach each other, in order to spring the two girders transversely of the longitudinal axis of said girders in the direction in which they will deform under the action of the service loads, maintaining the girders in their thus sprung position by screwed tighteners of ad justable length whose nuts have a curved face applied against a corresponding surface of the next portions of said adjoining ends, said curved surfaces having a circumference as section by a plane parallel to the plane in which the bending is effected, and supporting the proi0 jecting portions of said cross-pieces at such a level that the whole is at a distance from the ground.

9. A method for simultaneously springing two identical rigid metal girders by applying a moment thereto which will deform said girders transversely of their longitudinal axis in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precornpressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform in a direction transversely of the longitudinal axis of said girders under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these mean planes, arranging also said rigid metal girders in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said girders in a direction transverse to the longitudinal axis of said girders, maintaining locally the two girders at a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stiifening said girders in the proximity of said cross-pieces, bracing the stiffened portions of the girders and the projecting portions of the cross-pieces situated in their proximity, causing the adjoining ends of the girders to approach each other by a hydraulic jack mounted on a traverse through which pass two threaded rods carrying another traverse applied against one of the two girders, said jack acting on the remote faces of said ends, in order to spring the two girders transversely of the longitudinal axis of said girders in the direction in which they will deform under the action of the service loads, interposing between the piston of the hydraulic jack and one of the girders an arched support in order to permit a change in the angle of the end of the girder against which it is applied, maintaining the girders in their thus sprung position by means acting on the next portions of said adjoining ends, and support ing the projecting portions of said cross-pieces at such a level that the whole is at a distance from the ground.

10. A method for simultaneously springing two identical rigid metal girders by applying a moment thereto which will deform said girders transversely of their longitudinal axis in the direction in which they will be deformed by a service load preparatory to coating each girder with concrete to form a part of a beam of precompressed concrete and a thus sprung rigid metal girder, comprising arranging the two rigid metal girders in such a manner that their longitudinal mean planes in which they will deform in a direction transversely of the longitudinal axis of said girders under the effect of the service loads coincide and that they are symmetrical relatively to a plane perpendicular to these means planes, arranging also said rigid metal girders in such a manner that the ends of each girder are free to move towards each other under the application of a moment which will deform said girders in a direction transverse to the longitudinal axis of said girders, maintaining locally the two girders at a constant distance apart by interposition at a distance from their extremities, of cross-pieces projecting laterally relatively to the girders, stiffening said girders in the proximity of said cross-pieces, bracing the stiffened portions of the girders and the projecting portions of the crosspiece situated in their proximity, causing the adjoining ends of the girders to approach each other, by a hydraulic jack mounted on a traverse through which pass two threaded rods carrying another traverse applied against one of the girders, said jack acting on the remote faces of said ends in order to spring the two girders transversely of the longitudinal axis of said girders in the directions in which they will deform under the action of the service loads, guiding said threaded rods relatively to the hydraulic jack by means of a member movable with the piston of the latter and sliding along said threaded rods,

1 1 maintaining the girdersin, their thus sprung positian by means acting on thenext portions: of'said adjoining ends, and Supporting theiprojlecting portions of sai'd cross-pieces at such 'a level: that the whole. is at a distance from the ground.

References; Cited; in the. file of. this. patent V UNITED STATES PATENTS Knight Oct. 1, 1935 Stoehr May 6, 1941 'Cueni- Aug 14, 1945 Fouhy- Feb. 4, 1947 Coff June 13, 1950' FOREIGN PATENTS Great Britain Nov. 25, 1859 Switzerland 'Apr. 16,.1951 

